joejack951

Why would there be any difference between an outer chainring on a double and one for a triple? I only ask because when looking at swapping the outer ring on an FSA crankset, I noticed that on Universal Cycles website, they offer two different 50 tooth outer chainrings in the FSA Pro Road series. One is under the double section and one under the triple section. They have slightly different part numbers assigned. Any guesses?

enigmagic

The spiders are different...

I assume you noticed the different BCD on the triple vs. the double?

joejack951

In what ways?

enigmagic

Well, different cranks have different bolt circle diameter measures. That measure is the diameter of the circle that intersects the centres of the bolt holes in the chainring and applicable holes in the spider. Typical road triples are either 110BCD for the big rings and 74 for the granny or 130/74. Doubles can use either 110 or 130. It all depends on the cranks.


If you're asking the difference between the double and the triple with the same BCD and teeth its probably the design of the chainring, the ramps and pins and such may be a bit different, I'd think.

joejack951

Sorry, I should have been more specific. I am asking about an otherwise identical chainring (130mm BCD, same manufacturer, same series, same number of teeth) only one is spec'd for a double and one for a triple.

I could see the ramps and pins being different if one was designed to use a different size middle/inner ring but I don't think that's the case here. I'd expect to see two different version of the same ring for a double and two for a triple (Shimano does this with their A and B versions).

I just can't picture how shifting would be any different from a 39 tooth ring to a 50 tooth ring on a double than on a triple.

Mr. Underbridge

Maybe I'm nuts, but I was curious and went to check it out, and I didn't even see a 50t triple chainring. ??? Did see a double though.

Is this the link to the triple chainring?

https://www.universalcycles.com/shopp...&category=2629

joejack951

I meant to say 53 tooth chainring in my original post. The reason I was questioning the differences was because I wanted to use the 50 tooth chainring on a triple but they didn't offer a 50 tooth in the triple section.

That is the correct link BTW.

Gonzo Bob

Interesting! Perhaps there are differences in the ramps and pins or the tooth shape since the chainline for a triple is slightly different than for a double. I would think that they are interchangable without noticable difference. I also noticed that the 53 triple doesn't say whether it's for a 39 or 42 or 44 middle. Maybe the ramps and pins are placed to work with any of those.

Al1943

I think that all Shimano 53 triple big rings ran with 39 middle rings. 52 triple's were mated up with 42's and 39's.
I don't think the triple big rings have been designated "A" or "B", those are for doubles.
I don't know why triple big rings are different (if they are) from doubles but it may be because they are synchronized with middle rings that are synchronized with granny rings.
Supposedly if you're synchronized correctly the shifts will be smoother and quicker. But I wouldn't worry about that much, I think they're cross-compatible enough for most of us.

Al

TurboTurtle

Only thing that matters is the size of the next smaller ring. The pins and ramps are made to line up with a specific size. If all they say is 'triple' and 'double', you do not have enough information. They may assume that a double has a 39t inner ring and that a triple has a 42t middle ring, which was generally the case a few years ago but is not now. - TF

CaptainCool

I don't see any 50T rings on that link. Is it actually this one? It has different 50T rings depending on whether or not you're running Shimano 10-speed.
https://www.universalcycles.com/shopp...6&category=641

On FSA's site I found these:
https://www.fullspeedahead.com/fly.as...id=100&pid=155
https://www.fullspeedahead.com/fly.as...id=100&pid=156

Looks like the triple setup is supposed to use the same big ring as the double.

joejack951

I'm a little late getting back here but I just wanted to say thanks for all the replies. I think I finally figured out the difference in part numbers and I'm embarassed to admit how simple it is. The 53 big ring in the triple section is meant for Shimano 10 speed setups and the other two (one for a 39 and one for 42 inner) are both for Shimano 9 speed or Campy 9/10 speed. I'm not sure how I didn't notice this before.

So it seems like FSA only makes a Shimano 10 speed 53 big ring that will work with a 39 tooth inner yet their "original" 53 tooth chainrings are designed to handle a 39 or 42 depending on which one you choose. Makes a little bit of sense given what Al1943 said about Shimano's triples with 53 tooth outers always having 39 tooth inners.